1. Field of the Invention
The invention relates to a roll pressing machine, more particularly to a roll pressing machine for pressing a blank, such as a nut.
2. Description of the Related Art
As shown in FIGS. 1 and 2, a conventional roll pressing machine includes a pair of spaced apart rollers 83, and a conveying unit (not shown). When a normal nut 81 that has a screw hole 811 is conveyed to a position between the rollers 83, one end 812 of the nut 81 will be pressed by the rollers 83 so that the screw hole 811 tapers off at a portion 821 adjacent to the end 812 of the nut 81, thereby turning the nut 81 into a self-locking nut 82 (see FIG. 2) that can tightly engage a corresponding threaded rod (not shown) through the portion 821.
However, nuts 81 with a same specification may not have a uniform outer diameter due tounstable forming of the manufacturing process. Since the distance between the rollers 83 is fixed, when a plurality of the nuts 81 of the same specification are conveyed to the position between the rollers 83, the nuts 81 having a longer outer diameter will be pressed harder, and the extent that the screw holes 811 thereof contract will be large, thereby resulting in difficulty in engaging the threaded rod. Conversely, the extent that the screw holes 811 of the nuts 81 having a shorter outer diameter contract will be small due to less pressure applied thereto, thereby resulting in a poor locking effect.